Enhancing intermediate wheatgrass establishment in spotted knapweed infested rangeland

Abstract

The objective of this study was to compare intermediate wheatgrass establishment at 4 seeding rates, in combination with tillage and/or glyphosate (n-phosphomethyl glyine), in spotted knapweed infested rangeland. We hypothesized that the establishment of intermediate wheatgrass seedlings would be greatest at high seeding rates, while spotted knapweed density and biomass would be negatively impacted by intermediate wheatgrass densities. Glyphosate (1.16 liters a.i./ha; with and without), tillage (200 mm depth; with and without), and 4 seeding rates (0, 500, 2,500, 12,500 m-2) of intermediate wheatgrass seeds were factorially arranged in a randomized-complete-block design with 4 blocks at each of 2 sites in Montana. Treatments were applied in the fall of 1995. By the second growing season, intermediate wheatgrass failed to established in plots seeded with 500 seeds m-2, the currently recommended seeding rate. Increasing the seeding rate to 2,500 and 12,500 m-2 increased intermediate wheatgrass tiller density by 80 and 140 plants m-2, respectively, at Hamilton and 158 and 710 plants m-2, respectively, at Bozeman. At the highest seeding rate, combining tillage with glyphosate increased tiller density over 3 times more than other treatments where intermediate wheatgrass successfully established at Hamilton. However, neither tillage nor glyphosate affected intermediate wheatgrass density at Bozeman by the second growing season. In the first season, seeding rates of 0, 500, 2,500, 12,500 m-2 produced 214, 208, 176, and 114 knapweed plants m-2, respectively (LSD0.05 = 36.1) at Bozeman, but had no effect at Hamilton. Our revegetation study suggests that increasing intermediate wheatgrass seeding rates can facilitate their establishment in spotted knapweed infested rangeland. Using high seeding rates to control spotted knapweed and increase seedling establishment may enhance our ability to use revegetation as an effective weed management strategy.